Spread Spectrum Wireless Data Transceiver User Manual
Additional Transceiver information
This section contains additional important information about FreeWave transceivers. The following topics
are included in this section:
Operational RS422 and RS-485 Information
RS232 Pin Assignments
FGRO OEM Board Pin Assignments
FGR-115WC Waterproof Enclosure Pin out for 11-pin Waterproof Cable, part ASC0612WW.
Operational RS422 and RS-485 Information
For both RS-422 and RS-485, the FreeWave transceiver can drive 32 standard unit loads and loads the
bus with only 1/8 unit load. This means the user can tie up to 256 devices on the bus if all of the line
receivers have 1/8 unit load.
RS-422 is used for 4-wire or full duplex communication with one Master and multiple Slaves. The
FreeWave Master transceiver keeps the line driver asserted at all times. The maximum line length is
4,000 feet using a pair of 120 ohm twisted cables with a 5th wire for data common.
RS-485 full duplex using 4 wire plus common is the same as RS-422, except the system can have
multiple Masters on the bus.
The most common operation of RS-485 is a two-wire comprised of a 120 ohm impedance single twisted
pair. In this system the loading of the FreeWave transceiver is as described above which allows up to 256
1/8 unit load units on the bus. Maximum line length is also 4,000 feet with a third wire required for data
common. Before sending data, the FreeWave transceiver will check the line to be certain no other device
is transmitting before it enables its line driver for data transmission.
When setting the transceiver to RS-485, enable Modbus and set Master Packet Repeat to 3 in the
transceiver(s) that will use RS-485.
The Turn Off Delay setting in the menu is used to control the length of time the transmitter driver stays
asserted after data transmission has finished. This is needed to allow the last transmitted character to
reach the end of a long line and is normally set to one character length of time. This setting also allows 3
complete reflections to the end of the line to ensure the ringing on the line has fully dampened before
releasing the bus to another device. Shorter line lengths may use shorter delays, but four one-quarter-
character delay times are recommended. In Modbus, a Turn Off Delay setting of 0 will cause internal
timing errors.
There is no provision for hand shaking in any of the above modes of operation, so fast data rates of 57.6
K baud and above are not recommended without a protocol that can handle error detection properly.
LUM0002AD Version
6.1
53
